Hitherto, a member in which a terminal (connector) made of copper or a copper alloy (for example, brass) is attached to electrical wires composed of conductors of copper or a copper alloy, which is called a wire harness, has been used as an electrical wiring for movable bodies, such as automobiles, trains, and aircrafts. In weight reduction of movable bodies in recent years, studies have been progressing on use of aluminum or an aluminum alloy that is lighter than copper or a copper alloy, as a conductor for an electrical wiring.
The specific gravity of aluminum is about one-third of that of copper, and the electrical conductivity of aluminum is about two-thirds of that of copper (when pure copper is considered as a criterion of 100% IACS, pure aluminum has about 66% IACS). Therefore, in order to pass a current through a conductor of pure aluminum, in which the intensity of the current is identical to that through a conductor of pure copper, it is necessary to adjust the cross-sectional area of the conductor of pure aluminum to about 1.5 times larger than that of the conductor of pure copper, but aluminum conductor is still more advantageous than copper conductor in that the former has an about half weight of the latter.
Herein, the term “% IACS” mentioned above represents an electrical conductivity when the resistivity 1.7241×10−8 Ωm of International Annealed Copper Standard is defined as 100% IACS.
There are some problems in using the aluminum as a conductor of an electrical wiring for movable bodies.
First, in order to form such an aluminum alloy conductor into an electrical wiring material, the conductor is required to have such a workability that problems of wire breakage, strand displacement, and the like are not caused upon working, such as cold-drawing and twisting. When the workability of an aluminum conductor is poor, the producibility thereof cannot be enhanced, and wire breakage of the conductor in the use thereof as an electrical wiring material is concerned since the conductor poor in workability has forcedly been undergone wire-drawing and twisting, to result in a problem of lack of durability and reliability.
Second, there is a problem of improvement in resistance to bending fatigue. The reason why resistance to bending fatigue is required for an aluminum conductor that is used in an electrical wiring of a movable body is that a repeated bending stress is applied to a wire harness attached to a door or the like, due to opening and closing of the door. A metal material such as aluminum is broken by fatigue breakage at a certain number of times of repeating of applying a load when the load is applied to or removed repeatedly as in opening and closing of a door, even at a low load at which the material is not broken by one time of applying the load thereto. When the aluminum conductor is used in an opening and closing part, if the conductor is poor in resistance to bending fatigue, it is concerned that the conductor is broken in the use thereof, to result in a problem of lack of durability and reliability.
In general, it is considered that as a material is higher in mechanical strength, it is better in fatigue property. Thus, it is preferable to use an aluminum conductor high in mechanical strength. On the other hand, since a wire harness is required to be readily in wire-running (i.e. an operation of attaching of it to a vehicle body) in the installation thereof, an annealed material is generally used in many cases, by which 10% or more of tensile elongation at breakage can be ensured.
According to the above, for an aluminum conductor that is used in an electrical wiring of a movable body, a material is required, which is excellent in mechanical strength that is required in handling and attaching, and which is excellent in electrical conductivity that is required for passing much electricity, as well as which is excellent in workability and resistance to bending fatigue.
For applications for which such a demand is exist, ones of pure aluminum-systems represented by aluminum alloy wires for electrical power lines (JIS A1060 and JIS A1070) cannot sufficiently tolerate a repeated bending stress that is generated by opening and closing of a door or the like. Further, although an alloy in which various additive elements are added is excellent in mechanical strength, the alloy has problems that the electrical conductivity is lowered due to solid-solution phenomenon of the additive elements in aluminum, flexibility is lowered, and deterioration of workability is caused due to formation of excess intermetallic compounds in aluminum. Therefore, it is necessary to limit and select additive elements, to prevent lowering in electrical conductivity, lowering in flexibility and deterioration of workability, and to enhance mechanical strength and resistance to bending fatigue.
Typical aluminum conductors used in electrical wirings of movable bodies include those described in Patent Literatures 1 to 4. However, as mentioned below, the inventions described in the patent literatures each have a further problem to be solved.
Since the alloy described in Patent Literature 1 contains a relatively large amount of Fe as 1.10 to 1.50% and is free from Cu, the resultant intermetallic compounds cannot be suitably controlled, which results in deterioration in workability, and wire breakage in wire drawing and the like.
Since the invention described in Patent Literature 2 does not define any content of Si, it is necessary to further study the effects of the resultant intermetallic compounds (enhancement in mechanical strength, and improvement in resistance to bending fatigue, and heat resistance).
Since, in Patent Literature 3, the content of Si is large, the resultant intermetallic compounds cannot be suitably controlled, which results in deterioration of workability, and wire breakage in wire drawing and the like.
The alloy described in Patent Literature 4 contains 0.01 to 0.5% of antimony (Sb), and thus is a technique that is being substituted by an alternate product in view of environmental load.